The present invention relates to a unit for grasping and clamping a generally circular shaped part, comprising a central body on which three grasping and clamping elements are mounted adapted to bear tangentially on said part at three points or regions of tangential contact forming, pairwise, angles greater than 90.degree., one of the grasping and clamping elements being arranged to lie on the axis of said central body at one end of a movable central push rod, the other two said elements being arranged symmetrically with respect to said axis at the distal end of two levers each consisting of a clamping arm and an operating rod, each one of said levers being pivoted by the associated ends of said arm on a support shaft of said central body.
Units suitable for grasping parts are being used more and more for industrial robots and in the majority of cases consist of simple pincer-like grasping elements the jaws of which firmly clamp a strong metal part, by application of fluid pressure. An example of a grasping and clamping unit for a circular part is provided, for instance, in British Patent GB-A-2 089 707. In this document, a central body carries a central push rod and two rotatable levers, these three elements being actuated simultaneously by an axial fluid cylinder, during both clamping and release.
Known grasping and clamping devices are generally designed to handle metal parts requiring machining which are strong and to which significant clamping forces can be applied, ensuring that the workpieces to be manipulated are held firmly. When it is envisaged to handle disk-shaped parts, such as spectacle lenses in a fragile and brittle material, experience shows that known pincer-like clamping devices and grasping units are generally not satisfactory. They notably suffer from a risk of the part being accidentally dropped should there be an unintentional release of clamping fluid pressure. Moreover, they do not always enable the part to be correctly centered at the moment it is grasped, meaning that there is a constant danger of the part tipping over and becoming released.
One of the aims of the present invention is precisely that of providing a grasping unit which overcomes the above stated disadvantages and which further provides well-centered engagement of a disk-shaped part to be handled, together with permanent clamping action without the need to provide an external clamping force obtained for example by the use of fluid pressure, only unclamping or release being subject to the action of fluid pressure.